1. Field of the Invention
The present invention relates to an inductive head with an insulation stack whose height is reduced by a partial coverage zero throat height (ZTH) defining insulation layer and, more particularly, to an inductive head that has a ZTH defining insulation layer located entirely between an air bearing surface (ABS) of the head and one or more coil layers of an insulation stack, thereby permitting the insulation stack to be lowered.
2. Description of the Related Art
An inductive write head includes a coil layer embedded in first, second and third insulation layers (called xe2x80x9cthe insulation stackxe2x80x9d), the insulation stack being located between first and second pole piece layers. A gap is formed between the first and second pole piece layers by a gap layer at an air bearing surface (ABS) of the write head. The pole piece layers are connected at a back gap. Current conducted through the coil layer produces a magnetic field in the pole pieces. The magnetic field fringes across the gap at the ABS for the purpose of writing information in tracks on moving media, such as in circular tracks on a rotating magnetic disk or longitudinal tracks on a moving magnetic tape.
The second pole piece layer has a pole tip portion which extends from the ABS to a flare point, and a yoke portion which extends from the flare point to the back gap. The flare point is where the second pole piece begins to widen (flare) to form the yoke. The placement of the flare point directly affects the magnitude of a magnetic field produced to write information on the recording medium. Since the magnitude of magnetic flux decays as it travels down the length of the narrow second pole tip, shortening the second pole tip will increase the magnitude of the flux reaching the recording media. Therefore, performance can be optimized by aggressively placing the flare point close to the ABS.
Another parameter important in the design of a write head is the location of the zero throat height (ZTH). The zero throat height is the location where the first and second pole pieces first separate from one another after the ABS. ZTH separation is imposed by an insulation layer, typically the first insulation layer in the insulation stack. Flux leakage between the first and second pole pieces is minimized by locating the ZTH as close as possible to the ABS.
Unfortunately, the aforementioned design parameters require a tradeoff in the fabrication of the second pole tip. The second pole tip should be well-defined in order to produce well-defined written tracks on the rotating disk. Poor definition of the second pole tip may result in overwriting of adjacent tracks. A well-defined second pole tip should have parallel planar side walls which are perpendicular to the ABS. This definition is difficult to achieve because the second pole tip is typically formed along with the yoke after the formation of the first insulation layer, the coil layer and the second and third insulation layers. Each insulation layer includes a hard-baked photoresist having a sloping front surface.
After construction, the first, second and third insulation layers present front sloping surfaces which face the ABS. The ZTH defining insulation layer rises from a plane normal to the ABS at an angle (apex angle) to the plane. After hard baking of the insulation layers and deposition of a metallic seedlayer, the sloping surfaces of the insulation layers exhibit a high optical reflectivity. When the second pole tip and yoke are constructed, a thick layer of photoresist is spun on top of the insulation layers and photo patterned to shape the second pole tip, using a conventional photo-lithography technique. In the photo-lithography step, ultraviolet light is directed vertically through slits in an opaque mask, exposing areas of the photoresist which are to be removed by a subsequent development step. One of the areas to be removed is the area where the second pole piece (pole tip and yoke) is to be formed by plating. Unfortunately, when the ultraviolet light strikes the sloping surfaces of the insulation layers in a flaring region of the second pole piece, it is reflected forward, toward the ABS, into photoresist areas at the sides of the second pole tip region. After development, the side walls of the photoresist extend outwardly from the intended ultraviolet pattern, causing the pole tip plated therein to be poorly formed. This is called xe2x80x9creflective notchingxe2x80x9d. As stated hereinabove this can lead to overwriting of adjacent tracks on a rotating disk. It should be evident that, if the flare point is recessed far enough into the head, the effect of reflective notching would be reduced or eliminated since it would occur behind the sloping surfaces. However, this solution produces a long second pole tip which quickly reduces the magnitude of flux reaching the recording medium.
The high profile of the insulation stack causes another problem after the photoresist is spun on a wafer. When the photoresist is spun on a wafer, it is substantially planarized across the wafer. The thickness of the photoresist in the second pole tip region is higher than other regions of the head since the second pole tip is substantially lower on the wafer than the yoke portion of the second pole piece. During the light exposure step the light progressively scatters in the deep photoresist like light in a body of water, causing poor resolution during the light exposure step.
Although an insulation stack with a double coil is higher than an insulation stack with a single coil, a double coil head is desirable because two smaller diameter coils can produce the same flux density as a single coil, with less reluctance. Less reluctance permits a faster rise time of the signal which results in a faster data rate. There is a need for a double coil head wherein the height of the insulation stack can be reduced so as to improve the construction of a photoresist frame for plating the second pole tip.
Still another problem is that, if the ZTH defining layer of the insulation stack is not an insulation layer above the last coil, the ZTH will be altered by subsequent processing steps. A seedlayer, employed for plating the coil, is removed from all locations except under the coil by milling with an ion beam. The milling strikes all surfaces on a wafer where rows and columns of magnetic heads are constructed. If for instance, the ZTH defining layer is the first insulation layer of the insulation stack, removal of the seed layer will also remove part of the ZTH defining insulation layer. This will cause a recession of the original location of the ZTH defining insulation layer, which alters the design of the head.
The present invention does not employ any insulation layers of the insulation stack for defining the ZTH of the head. Instead a ZTH defining insulation layer is employed that is located entirely between the ABS and the one or more coil layers. The ZTH defining insulation layer is formed directly on the first pole piece, and has front and rear ends with a substantially flat top surface therebetween. The front end of the ZTH defining insulation layer causes the first and second pole pieces to first separate after the ABS, thereby defining the ZTH of the head. The first or only coil of the head is separated from the first pole piece by a thin layer of alumina which is the first insulation layer of the insulation stack. The first insulation layer is thinner than the ZTH defining layer so that the first or only coil layer is now lower than prior art coil layers. A bottom surface of the first or only coil layer is recessed below the top surface of the ZTH defining insulation layer. This makes the construction of a double coil head more desirable since the lower first coil will reduce the height of the stack. The double coil can be employed for increasing the data rate of the head, while the lower stack height will permit improved resolution of the second pole tip. When the photoresist is spun on the partially completed head the photoresist layer will be thinner in the pole tip region, reducing the scattering of light during an exposure step.
In a stitched head, with either a single or a double coil, reflective notching can be obviated, and resolution of the second pole tip can be improved. A stitched head is one in which the second pole piece has two components that are constructed separately. A second pole tip, located entirely between the ABS and the first or only coil layer, is constructed first, followed by a yoke portion that is connected (stitched) to a top surface of the second pole tip. The second pole tip is constructed on the ZTH defining insulation layer and has a back end that is forward of the rear end of the ZTH defining insulation layer. By locating a flare point of the second pole tip on the flat top surface of the ZTH defining insulation layer, all light in the light exposure step is reflected straight up instead of into photoresist regions adjacent a site for the second pole tip. Accordingly, there is no reflective notching. When the yoke portion of the second pole piece is constructed, reflective notching may occur, but this is unimportant since the second pole tip is already constructed. It should be noted that the height of the insulation stack in either the single or double coil stitched head will be reduced. This means that when the photoresist is spun on the head, it will be thinner in the pole tip region, permitting better resolution of the side walls of the photoresist frame for the second pole tip.
In a head including a single layer second pole piece with a single or double coil, reflective notching will be reduced by the present invention. In this case, the flare point is located in a flat section of the top surface of the ZTH defining insulation layer; as a result the second pole piece is flat from the flare point until it is forced to rise due to the insulation stack. Where the second pole piece is flat on the ZTH defining insulation layer, light will be directed upward during the light exposure step instead of into side regions of the photoresist frame where the pole tip is to be formed. Light is reflected from the insulation stack, far from the pole tip region, thereby reducing reflective notching. Further, the height of the insulation stack for either a single coil or a double coil will be reduced, thereby reducing the thickness of photoresist in the pole tip region. As stated hereinabove, this improves the resolution of the side walls and the bottom critical dimension of the second pole tip.
The invention also has other advantages. The gap layer can be employed both to form the gap layer between the pole tips, and to serve as the first insulation layer between the first or only coil and the first pole piece layer. Alternatively, an alumina layer may be formed on the ZTH defining insulation layer to serve as the first insulation layer for the insulation stack. After constructing the one or more coil layers, a portion of the alumina layer covering the ZTH defining insulation layer can be removed and a gap layer may be deposited. The second pole piece is then constructed on the gap layer. The advantage of this latter scheme is that the gap layer is not damaged when an ion beam is employed to remove one or more seed layers employed in the construction of the one or more coil layers. When a single alumina layer serves as both gap and first insulation layer, the layer must be provided with extra thickness in order to maintain a required gap thickness after process variations. In both schemes, however, the ZTH defining insulation layer is protected by a covering (an extra thick gap layer, or a removable alumina layer) so that the ZTH location is not altered by subsequent processing steps, such as removal of a coil seed layer by ion milling.
Another advantage of the invention is that the ZTH defining insulation layer can be extended by an appropriate photoresist frame to be located along the side edges of the first pole piece layer so as to minimize the height of the step from the top of the first pole piece layer to a second read gap layer. This improves planarity of a photoresist frame for the construction of the first coil layer. This planarity reduces or eliminates reflective notching of the coil frame so that when the coil is plated it will have well-defined side walls.
An object of the present invention is to provide an inductive write head with an insulation stack that has a reduced height.
Another object is to provide an inductive write head that has a second pole tip with improved definition.
A further object is to provide an inductive write head in which the zero throat height is not defined by any insulation layer of the coil insulation stack.
Still another object is to provide either a single or double coil stitched inductive write head with no reflective notching, and with improved resolution of the side walls of the second pole tip.
Still a further object it to provide either a single or double coil layer second pole piece inductive write head in which reflective notching is reduced and resolution of the side walls of the second pole tip is improved.
Still another object is to provide a method of making an inductive write head with an insulation stack that has a reduced height and, consequently, improved resolution of the side walls of the second pole tip.
Still a further object is to provide a method of making an inductive write head wherein, once a ZTH defining insulation layer is formed, the location of the ZTH is not altered by subsequent processing steps.
Other objects and advantages of the present invention will become apparent upon reading the following detailed description taken together with the accompanying drawings.